Disk drives generally utilize rotary actuators to position one or more magnetic read/write heads (also known as transducers), with respect to a similar number of magnetic disks rotatably mounted on a hub driven by a motor. The read/write heads are moved along selected tracks of the magnetic disks to gain access to the digital information record on that track and/or to write data to particular locations on the tracks. The read/write heads are mounted on an air bearing slider. The slider positions the read/write heads above the data surface of the disks by a cushion of air generated by the rotating disk. Alternatively, the slider may operate in contact with the surface of the disk. The slider is mounted to a suspension load beam or suspension arm assembly. The suspension maintains the read/write heads and the slider adjacent to or in contact with the data surface of the disk and preferably with as low a loading force as possible.
The suspension arm is connected to the distal end of a rotary actuator arm that is pivotally installed within the housing of the disk drive. Typically, the actuator arm is mounted by a pivot bearing assembly which allows the actuator arm to pivot in response to torques generated by a voice coil motor mounted to the yoke portion of the actuator arm.
Ideally, the pivot bearing assembly provides a nearly frictionless pivot for the actuator thereby allowing the actuator to be precisely controlled for movement across the surface of the disk. It is desirable that the pivot bearing assembly have a high radial and axial stiffness, yet maintain a very low rotational stiffness thereby ensuring the actuator has adequate track following capabilities. As track densities increase to meet higher product capacities, improved dynamic performance of the actuator is required in order to increase the bandwidth of the servo loop. Drive servo performance is largely determined by servo bandwidth, which is dictated by the dynamic performance of the actuator. The most prominent bandwidth limiting characteristic in a disk drive is typically the system mode of the actuator which inherently has some amount of uncontrollable vibration. Increasing a pivot bearing assembly's radial stiffness increases system mode frequency and thereby improves the bandwidth capability of the disk drive.
A conventional pivot bearing assembly typically includes a central pin or shaft, one or more inner races, corresponding outer races, wherein the races coaxially surround the shaft. Ball bearings are located between the races and are sealed with respect to the races. With such conventional bearings, the radial stiffness of the bearings is derived from radial contact forces between the ball bearings and the races. As well understood by those skilled in the art, in order for a conventional bearing to function with low rotational resistance, the ball bearings cannot be tightly jammed against the race surfaces, and rather, there must be some defined gap between the ball bearings and races which allow at least some rotation of the ball bearings in the races in order to provide minimal frictional interference for rotation of an outer race about an inner race. Thus, some amount of looseness or “play” exists for such conventional bearings. As such, from a design standpoint, the need for low rotational resistance is in conflict with the need for high radial stiffness.
There are three conventional approaches to assembling the pivot assembly to the actuator body. One approach is to use a screw to pull or push the pivot assembly against the actuator bore. Another approach is to bond the pivot assembly to the actuator bore. Yet another approach is to conduct a press fit with an interposing device such as a tolerance ring. Each approach offers advantages and disadvantages. The screw attach bearing is easy to rework but has low stiffness. The bonded approach has high stiffness but is nearly impossible to rework. The press fit between the bearing and the bore of the actuator can create particulate contamination due to scoring and scraping of the outer race against the bore which inherently occurs when the bearing is press fit and reverse pressed during removal.
Based upon the shortcomings of the prior art, there is a need for a pivot bearing that is of simple construction, yet can accommodate increased drive performance requirements by increasing overall stiffness of the bearing, and particularly radial stiffness of the bearing. Additionally, there is a need to provide a bearing construction which accommodates rework by minimizing contamination. It is also preferable to design a pivot bearing that requires a minimal amount of torque to rotate the actuator. Therefore, it is not desirable to sacrifice the advantages of a nearly frictionless bearing by increasing overall bearing stiffness with increased bearing friction.